[sdiy] [Slightly OT] Op-amp headroom in synth & audio applications

[David G Dixon]

If you run a filter with a robust input signal, and have resonance set close
to oscillation, then even a nominally 10Vpp signal can generate voltages at
or near the rails.  If your signal is already near the rails, then anything
out of the ordinary will clip and distort.  That's my take, anyway.  I like
headroom.

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl 
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Justin Owen
> Sent: Tuesday, March 10, 2015 11:21 AM
> To: SDIY List
> Subject: [sdiy] [Slightly OT] Op-amp headroom in synth & 
> audio applications
> 
> Hope nobody minds these couple of slightly OT posts - just 
> know I'll get a good answer here!
> 
> I've been wondering about power supplies vs. output signals 
> on different formats and it seems there's a lot of 'spare' headroom...
> 
> MOTM: +/-15V supply  w/- audio output of +/-10V (20V PP) i.e. 
> output is 67% of supply
> 
> System 500: +/-16V w/- peak transients at approx. +18dBu or 
> approx. +/-8.7 (17.4 V PP)  i.e. output is 54% of supply
> 
> Eurorack: +/12V supply w- with audio output of +/-5V (10V PP) 
> =  i.e. output is 42% of supply!
> 
> I understand that there's a margin for staying away from the 
> rails and for the tolerances of parts like VRegs and what not 
> and maybe part of it is a hangover from the days of less 
> efficient amps - but considering that a good op-amp like the 
> OPA134 will (according to the data sheet) operate down to 
> +/-2.5V and work-horse amps like the TL072 aren't far behind 
> that - why so much headroom?
> 
> Just curious - thanks,
> 
> - J
> 
> 
> 
> 
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